The recent escalations in the costs of petroleum products and other types of fuel have focused great attention on means for conserving energy. One area of significant potential savings in energy is in the energy used to heat and cool buildings such as residential homes. The two major sources of energy loss in buildings are themal conduction through walls, ceilings and floors, and infiltration of air where, for example, warm inside air is displaced by cold outside air through cracks, holes and other openings in the structure of the building. Techniques for minimizing energy losses by conduction in both new and old buildings are well known (insulating materials of various kinds, storm windows and doors, etc.) and has been well publicized both by public service agencies and commercial manufacturers.
On the other hand, it is not nearly as generally appreciated that in most buildings, new or old and with or without adequate insulation, air infiltration is still a major source of heat loss. According to one estimate, from 15 to 67% of the total heating energy utilized in residential buildings is due to the infiltration of air. Furthermore, with the exception of weatherstripping around doors and windows and exterior caulking, it is still not general practice in new residential construction to build with a goal of reducing air infiltration to the minimum practical level. Older houses, built in the era of cheap energy, are even worse in this regard.
Techniques to minimize air infiltration are known and in general are relatively inexpensive to accomplish. In order to promote the more widespread application of these techniques and to thereby capitalize on the potential energy savings realized by the use of these techniques, a simple and economical testing device to measure air infiltration in residential homes and other buildings should be made widely available. To be effective, such a testing device should be able to quickly determine how serious a problem air infiltration is in a given structure, and also should be capable of indicating the effectiveness of the steps taken to reduce the air infiltration.
An instrumental technique known as a gas or fan pressurization has been used for estimating the resistance of enclosures to air infiltration. In this technique, a device having a variable-speed fan is utilized to establish a given pressure differential between the interior and exterior of the enclosure and the flow rate through the fan is then measured. Although it is the air leakage at low (weather-induced) pressures (-5 Pa&lt;.DELTA.P&lt;5 Pa) that is needed to model infiltration, the pressure differences induced by fan pressurization typically range between .+-.10 to .+-.50 Pa. The tests are made at higher pressures because weather-induced pressures interfere with measurements and thus cause large measurement uncertainties at low pressures. This lack of precision at low pressures is one of the major disadvantages of the fan pressurization technique.
In Lawrence Berkeley Laboratory report No. LBL-9162 entitled "THE LOW PRESSURE LEAKAGE FUNCTION OF A BUILDING" by M. H. Sherman, D. T. Grimsrud and R. C. Sonderegger (November 1979), a method for measuring the air leakage in buildings was described which utilized alternating pressurization. With this technique, measurements were made at pressures similar to natural conditions rather than at artificially high pressures required by fan pressurization techniques. The device described in the report comprised a large piston and guide and sleeve assembly that was installed in place of the existing exterior door. A motor and crank mechanism moved the piston back and forth within the guide, pumping air in and out of the building.
Another report entitled "Infrasonic Measurement of Building Air Leakage: A Progress Report" by W. H. Card et at, ASTM Special Technical Publication No. 719, also investigated alternating pressurization as a means of qualifying tightness. However, neither of these approaches outlined above, among other things, was able to produce an apparatus which could produce an accurate real-time determination of tightness of an enclosure nor an apparatus that could be used easily and conveniently.